One method to control an internal combustion engine and a power take off device is described in U.S. Pat. No. 5,611,751. This method presents a means to control transitions between first and second operating modes. In the first operating mode, engine power is inhibited from the power take off (PTO) device output. In the second operating mode, at least a portion of engine power is permitted to flow to the PTO device output. The method controls transitions between operating modes based on operator input to several switches.
In another aspect of the before-mentioned patent, a method is provided to enter an operating mode where engine power flows to a PTO device output, after operating in a mode where engine power is inhibited from the PTO device output. This method allows an operator to manually set a target engine speed by depressing an accelerator or by pressing a resume switch which allows an engine controller to read a previous engine speed operating point from memory and then use the previous engine speed as a target engine speed.
The above-mentioned methods can also have disadvantages. Namely, the method can transition from one operating mode to another, in response to operator inputs, without regard to the PTO load or engine torque capacity. In other words, if an operator fails to follow a specific power take off operating sequence, he or she may cause the engine to stall since the PTO may be engaged to the engine at a lower engine operating speed where the amount of available engine torque may be less than an amount necessary to turn the engine and the PTO load. Further, controlling the engine based on a single PTO operating condition, namely, PTO speed, can result in transient engine air-fuel errors and deviation from the desired engine speed during mode or operating point transitions.
The inventors herein have recognized the above-mentioned disadvantages and have developed a system and method that offers substantial improvements over previous systems and methods.